The invention relates to the dimeric compound of formula (II) wherein the two monomer-units are linked with each other either via R3 or via R4; the ring A is a five-or six-membered heteroaromatic ring, one of the groups R3 or R4 is an unsubstituted or substituted phenylene radical, the remaining group R3 or R4 is a C1-C4 alkyl, C5-C6 cycloalkyl, an unsubstituted or substituted phenyl, benzyl, benzanilide or naphthyl; or wherein the group NR4 together with the ring A constitutes a five-or six membered heterocycle that can be annelated with a benzene ring, and R3 is an unsubstituted or substituted phenylene radical. The inventive compounds can be used for pigmenting high-molecular organic materials.